Study On The Corrosion Behaviors Of Zr-Cu-(Nb)-Ag-Al-Be Bulk Metallic Glasses

Zr-based bulk metallic glasses (BMGs) exhibit excellent glass forming ability (GFA), high thermal stability, high strength and low elastic module. Howere, the high susceptibility of Cl- induced pitting limits the application as biomedical materials or used in hostile environments. Therefore, we performed a systematic research to improve the corrosion resistance to Cl- of Zr-Cu-(Nb)-Ag-Al-Be BMGs. The following are our mainly achieved results:(1) Deterioration of GFA and evident improvement on corrosion resistance were observed after substitution of Nb for Cu. In 0.5 M NaCl solution:Nb-frree BMG don’t passivated to Cl-, corrosion potential (Ecorr) and pitting potential (Epit) were obviously increased by Nb added; Cu dissolved deferentially in Cl-contained solution, Nb addition significantly restrained the dissolve of Cu and suppressed the nucleation of pits. X-ray photoelectron spectroscopy analysis show:Zr, Al and Be enriched in surface; layer structure were were found of nature formed oxide film that ZrO2, BeO, Al2O3, Cu2O, Ag2O and Nb2O5 form outer layer, NbO2, NbO, ZrO, Zr2O and metallic atoms constitute middle layer, metallic matrix and protoxide of Zr make up inner layer; higher Nb content and numerous hydroxide contained passive film were formed in immersion test, Nb chemical state oxidized from Nb4+ and Nb5+ in nature formed flim to Nb5+ completely. Thus, Nb-contained BMG formed denser oxide film because of the compressive stress induced by Nb2Os, dissolution of Cu and diffusion of Cl-were effectively constrained.(2) After thermal oxidization:thickness with 0.3～0.4μm and Al, O enriched oxide layer were formed at surface; Ecorr and Epit of Nb-contained BMG were evidently enhanced, while Nb-free BMG don’t show apparently change; surface pit density of BMGs in immersion test both decreased and Cu enrichment and Zr depletion were found inside pits. Except Nb2O5 exist and lower Cu content in Nb-contained BMG surface, other elements are similar with Nb-free BMG from X-ray photoelectron spectroscopy analyzes. Nb2O5-contained oxide film is more denser and Cl- diffusion was more effectively impeded caused greater improvement of corrosion resistance on Nb-contained BMG after oxidization.